DMT-MM mediated functionalisation of the non-reducing end of glycosaminoglycans

Efficient functionalisation of the non-reducing end of uronic acid derivatives and glycosaminoglycan-derived disaccharides using peptide coupling has been achieved, mediated by the water-soluble agent DMT-MM.     

AFM nanoindentations of diatom biosilica surfaces

Diatoms have intricately and uniquely nanopatterned silica exoskeletons (frustules) and are a common target of biomimetic investigations. A better understanding of the diatom frustule structure and function at the nanoscale could provide new insights for the biomimetic fabrication of nanostructured ceramic materials and lightweight, yet strong, scaffold architectures. Here, we have mapped the nanoscale mechanical properties of Coscinodiscus sp. diatoms using atomic force microscopy (AFM)-based nanoindentation. Mechanical properties were correlated with the frustule structures obtained from high-resolution AFM and scanning electron microscopy (SEM). Significant differences in the micromechanical properties for the different frustule layers were observed. A comparative study of other related inorganic material including porous silicon films and free-standing membranes as well as porous alumina was also undertaken.     

Strategies in two‐dimensional liquid chromatographic separation of complex polymer systems

Complex synthetic polymer systems as for example copolymers exhibit distributions in at least two of the three basic molecular characteristics which are molar mass, chemical structure/composition and molecular architecture. Size exclusion chromatography (SEC) separates macromolecules according to their size in solution which simultaneously depends on all molecular characteristics. Therefore, multi‐dimensional liquid chromatographic techniques are to be applied to independently assess all different distributions present in the sample. So far, two‐dimensional separations have been attempted. In the first dimension separation column, selected liquid chromatographic mechanisms are intentionally combined to suppress effects of all but one molecular characteristic. Consequently, polymer species are separated exclusively or at least predominantly according to one single parameter. In the second dimension separation column, macromolecules are separated according to another molecular characteristic. In this contribution the methods are briefly reviewed in which effect of polymer molar mass on polymer retention is suppressed. The resulting ”one parameter separation systems” can be on‐line or off‐line connected to another separation system such as SEC to provide more detailed characterization of complex polymers. Besides, selected procedures for the re‐concentration of diluted polymer solutions are concisely treated. These may be utilized for increasing the concentration of sample(s) leaving the first dimension separation column. Eventually, some arrangements for controlled sample re‐introduction into the second dimension separation column are outlined.     

Biodegradable hybrid polymer films based on poly(vinyl alcohol) and collagen hydrolyzate

Hybrid blends of poly(vinyl alcohol) (PVA) and collagen hydrolyzate (CH), an added value waste from leather indutry, have been converted by blown molding extrusion, to environmentally degradable films. Blown extruded films comprising 5-15% of CH, were tested as sel fertilizing mulching films and analyzed for their propensity to enviromental degradation. PVA/CH films rapidly disintegrate when buried in soil, and resulted promising for application such as transplanting films, with additional fertilizing action of CH.     

A simple approach for synthesis of TiO2 nanotubes with through‐hole morphology

The present work reports a simple approach for fabrication of self‐standing titania (TiO₂) nanotube membranes with through‐hole morphology. The method is hydrofluoric acid free and the pore opening of TiO₂ nanotubes is performed by electrochemical thinning of the oxide barrier layer. A reduction of anodization voltage was applied at the end of the anodization process to cause a successful removal of the remaining barrier layer from the TiO₂ nanotubes during their detachment from the underlying titanium substrate. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Preparation of Cyclodextrin–Iron Species in Water by Laser Ablation: Secondary Ion Mass Spectrometry

Supramolecular complexes between cyclodextrin and iron species are studied by using secondary ion mass spectrometry. The iron species are prepared by pulsed‐laser ablation of bulk iron in water; this gives Fe⁺ (56 m/z) and Fe_xO_y⁺ (x, y=1–7) species. Cyclodextrin is added to the water either before or after the laser ablation. When it is added before laser ablation, molecular fragments of cyclodextrin are detected as dehydrated glucopyranose units (C₆H₈O₄⁺) associated with Fe⁺, FeO⁺, and Fe₂O⁺ species. The focus is to observe supramolecular host–guest complexes or adducts between intact molecules of cyclodextrin and iron species. When cyclodextrin is added after laser ablation, the relevant peak at 1210 m/z is observed and assigned as C₄₂H₆₇O₃₅FeNa⁺, which corresponds to a cyclodextrin molecule minus three H atoms. Two possible explanations of this finding are the presence of the host–guest C₄₂H₆₇O₃₅Na–Fe complex, in which Fe is in the cavity, or the presence of the adduct C₄₂H₆₇O₃₄Na–FeO with FeO on the outer surface; the formation of these complexes are supported by the hydrophobicity of Fe and hydrophilicity of FeO, respectively. Due to the presence of 12 % of intact C₄₂H₇₀O₃₅Na–Fe complex and an estimated Fe/FeO ratio of approximately 10², host–guest formation is assumed to be more significant.     

Thermodynamics of interactions of vancomycin and synthetic surrogates of bacterial cell wall

Glycopeptide antibiotics, including vancomycin, form complexes via a set of five hydrogen bonds with the acyl-l-Lys-d-Ala-d-Ala portion of the peptidyl stems of the bacterial cell wall peptidoglycan. This complexation deprives the organism from the ability to cross-link peptidyl stems of the peptidoglycan, leading to bacterial cell death. Four synthetic fragments as surrogates of the components of the bacterial cell wall have been prepared in our lab in multistep syntheses. These synthetic samples were used in investigations of the thermodynamics properties (DeltaG degrees , DeltaH degrees , and TDeltaS degrees ) for the complexation with vancomycin by isothermal titration calorimetry (ITC). Complexation with the glycopeptide analogues is largely enthalpy-driven (formation of five hydrogen bonds), and in the analogues with a single peptidyl stem, the complexation is 1:1. The complexation is more complicated with an approximately 2 kDa cell wall surrogate (compound 4), which possesses two peptidyl stems. The data were suggestive of interactions between the two vancomycin molecules, with an entropic penalty attributable to restriction of molecular movements within the complex due to restriction of motion of the highly mobile acyl-d-Ala-d-Ala moiety of the peptidyl stems. These data were reconciled with the recently determined NMR solution structure for the peptidoglycan fragment 4 and its implications for the larger cell wall.     

Facile carbon-fluorine bond activation and subsequent functionalisation of 1,1-difluoroethylene and tetrafluoroethylene promoted by adjacent metal centres

The bridging fluoroolefin ligands in the complexes [Ir(2)(CH(3))(CO)(2)(μ-olefin)(dppm)(2)][OTf] (olefin = tetrafluoroethylene, 1,1-difluoroethylene; dppm = μ-Ph(2)PCH(2)PPh(2); OTf(-) = CF(3)SO(3)(-)) are susceptible to facile fluoride ion abstraction. Both fluoroolefin complexes react with trimethylsilyltriflate (Me(3)SiOTf) to give the corresponding fluorovinyl products by abstraction of a single fluoride ion. Although the trifluorovinyl ligand is bound to one metal, the monofluorovinyl group is bridging, bound to one metal through carbon and to the other metal through a dative bond from fluorine. Addition of two equivalents of Me(3)SiOTf to the tetrafluoroethylene-bridged species gives the difluorovinylidene-bridged product [Ir(2)(CH(3))(OTf)(CO)(2)(μ-OTf)(μ-C=CF(2))(dppm)(2)][OTf]. The 1,1-difluoroethylene species is exceedingly reactive, reacting with water to give 2-fluoropropene and [Ir(2)(CO)(2)(μ-OH)(dppm)(2)][OTf] and with carbon monoxide to give [Ir(2)(CO)(3)(μ-κ(1):η(2)-C≡CCH(3))(dppm)(2)][OTf] together with two equivalents of HF. The trifluorovinyl product [Ir(2)(κ(1)-C(2)F(3))(OTf)(CO)(2)(μ-H)(μ-CH(2))(dppm)(2)][OTf], obtained through single C-F bond activation of the tetrafluoroethylene-bridged complex, reacts with H(2) to form trifluoroethylene, allowing the facile replacement of one fluorine in C(2)F(4) with hydrogen.     

Long-term correlations in hourly wind speed records in Pernambuco, Brazil

We study the statistical properties of hourly wind speed time series detected at four weather stations in the state of Pernambuco, Brazil, in the period 2008-2009. We find that the average and maximum hourly wind speeds deviate from a mutual linear relationship, and that they may be well explained individually by a Weibull distribution, however, with different shape parameter values. On the other hand, the long-term correlations of both of these observables obey the same power-law behavior, with two distinct scaling regimes. Our results agree with previous studies on wind speed series correlations in other regions of the world, which is suggestive of universal behavior.     

Facile Carbon–Fluorine Bond Activation and Subsequent Functionalisation of 1,1‐Difluoroethylene and Tetrafluoroethylene Promoted by Adjacent Metal Centres

The bridging fluoroolefin ligands in the complexes [Ir₂(CH₃)(CO)₂(μ‐olefin)(dppm)₂][OTf] (olefin=tetrafluoroethylene, 1,1‐difluoroethylene; dppm=μ‐Ph₂PCH₂PPh₂; OTf^?=CF₃SO₃^?) are susceptible to facile fluoride ion abstraction. Both fluoroolefin complexes react with trimethylsilyltriflate (Me₃SiOTf) to give the corresponding fluorovinyl products by abstraction of a single fluoride ion. Although the trifluorovinyl ligand is bound to one metal, the monofluorovinyl group is bridging, bound to one metal through carbon and to the other metal through a dative bond from fluorine. Addition of two equivalents of Me₃SiOTf to the tetrafluoroethylene‐bridged species gives the difluorovinylidene‐bridged product [Ir₂(CH₃)(OTf)(CO)₂(μ‐OTf)(μ‐C?CF₂)(dppm)₂][OTf]. The 1,1‐difluoroethylene species is exceedingly reactive, reacting with water to give 2‐fluoropropene and [Ir₂(CO)₂(μ‐OH)(dppm)₂][OTf] and with carbon monoxide to give [Ir₂(CO)₃(μ‐κ¹:η²‐C?CCH₃)(dppm)₂][OTf] together with two equivalents of HF. The trifluorovinyl product [Ir₂(κ¹‐C₂F₃)(OTf)(CO)₂(μ‐H)(μ‐CH₂)(dppm)₂][OTf], obtained through single C? F bond activation of the tetrafluoroethylene‐bridged complex, reacts with H₂ to form trifluoroethylene, allowing the facile replacement of one fluorine in C₂F₄ with hydrogen.